In recent years, there has been increasing demand for portable electronic products such as laptop computers, smartphones, and smartwatches, and the development of devices such as energy storage batteries, robots, and satellites has begun in earnest. Along with this, research into high-performance secondary batteries that can be repeatedly charged and discharged has been more actively conducted.
Examples of currently commercialized secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, and lithium secondary batteries. Among such various secondary batteries, lithium secondary batteries are freely rechargeable because of having substantially no memory effect compared with nickel-based secondary batteries, and have a very low self-discharge rate and high energy density. Owing to these merits, there has been high interest in lithium secondary batteries.
In general, lithium secondary batteries use a lithium-based oxide as a positive electrode active material and a carbonaceous material as a negative electrode active material. A lithium secondary battery may include: an electrode assembly in which a positive electrode plate coated with such a positive electrode active material and a negative electrode plate coated with such a negative electrode active material are disposed with a separator therebetween; and a case, that is, a battery case in which the electrode assembly and an electrolytic solution are sealed.
In general, according to case types, lithium secondary batteries may be classified into a can type in which an electrode assembly is accommodated in a metal can, and a pouch type in which an electrode assembly is accommodated in a pouch formed of an aluminum laminate sheet.
In recent years, secondary batteries have been widely used not only in small-sized devices such as portable electronic devices, but also in medium to large-sized devices such as automobiles or power storage devices. In particular, along with the depletion of carbon energy and the increasing interest in the environment, there has been worldwide interest in hybrid vehicles and electric vehicles in countries such as the USA, Europe, Japan, and Korea. The core component of such a hybrid or electric vehicle is a battery pack providing driving power to a vehicle motor. Since hybrid or electric vehicles can have driving power via charging and discharging of battery packs, hybrid or electric vehicles have high fuel efficiency and emit no pollutants or less pollutants compared to vehicles only using engines, and thus the use of hybrid or electric vehicles has been gradually markedly increased.
Most battery packs, particularly, middle to large-sized battery packs for hybrid vehicles, electric vehicles, or energy storage systems (ESSs) include a plurality of secondary batteries, and the plurality of secondary batteries are connected in series and/or parallel with each other for high capacity and power. In addition, pouch-type secondary batteries are generally used in middle to large-sized battery packs because the pouch-type secondary batteries are easy to stack and are light, and a large number of pouch-type secondary batteries can be included in one battery pack.
Electrical connection between pouch-type secondary batteries are generally achieved by bringing electrode leads into direct contact with each other. In this case, electrode leads having the same polarity are connected to each other so as to connect secondary batteries in parallel to each other, or electrode leads having different polarities are connected to each other so as to connect secondary batteries in series to each other.
However, if electrode leads that should not be connected to each other are connected, an internal short circuit may be formed, damaging a battery pack and even causing fire or explosion. On the other hand, if electrode leads that should be connected to each other are separated from each other, power may not be properly supplied from a battery module, causing a power insensitive phenomenon or decreasing the capacity or power of the battery module. As described above, if a phenomenon such as a power insensitive phenomenon occurs, a device including a battery module such as an automobile may not operate, and in this case, a big accident may occur.
Therefore, it is required to stably maintain contact between electrode leads in an intended manner without unintended contact or separation. In addition, battery modules for automobiles may be frequently exposed to vibrations or shocks, and thus it has been constantly required to develop a battery module capable of stably maintaining connection between electrode leads even when the battery module is vibrated or impacted.
In addition, it is required to guarantee the assemblability of battery modules in addition to stably maintaining connection between electrode leads of the battery modules. For example, if it is very difficult to assemble battery modules even though connection between electrode leads is stable, the productivity of the battery modules may decrease, and the possibility of defects in the battery modules may increase.
In particular, a battery module may include a sensing bus bar to sense voltages of secondary batteries, and to this end, the sensing bus bar may have to be in contact with an electrode lead. In this case, an electrode lead may have to be in contact with another electrode lead and a sensing bus bar as well. Therefore, when a battery module is assembled, a structure imparting high assemblability to a connection portion between an electrode lead and a sensing bus bar may be required to facilitate connection between electrode leads and connection between an electrode lead and a sensing bus bar. Furthermore, a coupling process such as a welding process may be performed so as to stably maintain connection between a plurality of electrode leads and a sensing bus bar, and in this case, a module structure having high weldability is preferred.